log (S_8.0/S_4.5) − log  (S_5.8/S_3.6) diagram. In gray is shown the entire zCOSMOS-20k sample, in violet the morphological ETGs, in light red the red-sequence galaxies, in dark red the red UVJ galaxies, in pink the red SED galaxies, in orange the quiescent galaxies, and in yellow the red & passive ETGs. The upper plot shows the log (S_8.0/S_4.5) − log  (S_5.8/S_3.6) diagram obtained for z ≤ 0.5, and the lower plot shows the diagram obtained for z > 0.5. The gray hatched area represents the region that falls outside the passive region of the IRAC color−color diagram, as defined in Sect. 3.1. The dotted lines represent the region defined by Lacy et al. (2004) to identify AGN candidates, and the dashed lines the revised definition by Donley et al. (2012). The representative errorbar for both quantities is shown in the bottom right corner.